This invention relates to model airplanes, specifically to an automatic pilot system comprising independent novel rudder, elevator, and wing tip means for automatically guiding the aircraft on a circular flight path following a high-speed take-off in a straight line, automatically adjusting the angle of attack, and providing enhanced lateral stability for the aircraft, respectively.
Many flying toys and model airplanes, such as gliders, are launched with the help of an expanded elastic band that is connected to the airplane through a hook. Upon contraction, the elastic band propels the airplane to fly. The towing results in a high-speed take-off in a straight line. Upon release, however, it is desirable that the glider follow a circular flight path at a lower speed to facilitate a longer gliding time and an easier retrieve upon landing.
Such a flight pattern is achieved on radio-controlled model gliders by the pilot who must actively and continuously adjust the rudder and elevator positions, both while the glider is being towed in a straight path, and while it is gliding slowly in ample circles. However, it is desirable to achieve a similar flight performance with gliders that have no complicated expensive radio control components.
Several U.S. Patents have been granted for mechanisms that work as a limited, or incomplete automatic pilot system for model gliders. However, they do not produce a flight performance that is comparable to that of a radio-controlled plane.
Some of the pilot systems found in the prior art include means for controlling the flight path by adjusting only the elevator position, such as U.S. Pat. Nos. 1,300,564; 2,588,941; 2,597,521; 2,820,322; 3,995,310; 3,995,393; 4,282,675; 4,375,138 and 5,383,805. These systems typically consist of multiple parts, such as hinges, links, rubber bands, elastic time delay mechanisms etc. While they make the glider""s transition from a steep climb to a level glide possible, they do not provide automatic directional control for the rudder, hence the glider can only fly in a straight path.
Some small model gliders, launched by a slingshot, utilize the elevators to achieve a circling gliding flight. For example, to make the glider turn left, the left side elevator is bent up, while the right side elevator is bent down. To provide the transition from the steep climb to the level glide, the nose-weight of the glider is adjusted. There are two main disadvantages of this control system: (a) to obtain a fast, steep climb followed by a smooth circling glide, the user is required to have a skillful coordination between orienting the glider""s roll angle, aiming the slingshot, and controlling the amount of stretch given to the rubber band, (b) the glider can be launched only to low heights, since this control system cannot be used in combination with a long elastic tow line.
Other mechanisms found in the prior art, achieve the transition from the high speed launch to the low speed glide by changing the position of the main wings, while keeping the position of the elevators unchanged. For example, U.S. Pat. No. 4,125,960 uses an airflow sensor which, upon deceleration, automatically slides the main wings of the glider towards the nose. In U.S. Pat. Nos. 4,836,817 and 4,863,412, both the left, and right wings are rotated to be aligned with the rudder for take-off, and they are held in that position by the air pressure of a fast slingshot launch. After a near vertical climb the glider slows down and a rubber band forces the wings to rotate back to their normal flying positions. The three main disadvantages of these control systems are: (a) they do not provide any directional control since the rudder remains fixed during the launching and gliding phases, (b) they do not make the transition from high speed to low speed a smooth one; generally there is a nose dive or a looping flight before a stable gliding flight is achieved, and (c) they are complicated to manufacture and assemble since they are made of multiple components, such as rubber bands, hinges, links etc.
Still other mechanisms found in the prior art, such as U.S. Pat. No. 2,876,585, control the elevator position by means of a small auxiliary vertical fin, parallel to the rudder. This system provides the necessary means for transition from a fast climb to a low-speed glide and also some directional control, since the auxiliary fin makes the airplane turn. However, this mechanism has four disadvantages: (a) it can only turn the plane in a fixed direction, either left or right, (b) it can provide only slight turning, since the rudder itself is not being controlled, (c) it cannot control the amount of turning independently of the gliding angle of the aircraft, since the positions of the elevator and the auxiliary fin are designed to be linked together, and (d) it is complicated to manufacture and assemble since it is made of multiple elements, such as rubber bands, linkages and active aerodynamic surfaces.
The lateral stability of model aircraft during flight can be enhanced by wings that have larger than zero dihedral angles. Usually, model gliders have wings with dihedral angles of up to about 10 degrees. Having wings with relatively large dihedral angles helps to recover quickly from turbulent gusts of wind. On the other hand, wings with excessive dihedral angles tend to overcorrect, resulting in lateral oscillations, instead of a level flight. In the prior art, increased lateral stability has been frequently added to the glider by rigid wing tips having fixed dihedral angles in the range of about 20-30 degrees. However, these wing tips change the effective dihedral angles of the wings to another fixed value, which cannot be adjusted according to the prevailing flight conditions.
Accordingly, it is an object of the present invention to provide an automatic pilot system for model aircraft that avoids the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide an automatic pilot system for model aircraft, such as gliders that:
(a) provides full three-axis automatic controllability for the aircraft by having independently movable elevator, rudder, and wing tip components, wherein those components have means for continuously sensing the relative wind speed and means for self-adjusting the positions of their control surfaces accordingly;
(b) does not require radio control or external power to actuate the elevator, the rudder, or the wing tip control surfaces;
(c) makes it possible for the aircraft to climb in a straight path and glide in a circular path;
(d) provides a smooth transition from a high-speed climbing to a low speed gliding;
(e) has control elements that comprise no complicated multiple components, such as rubber bands, hinges, links etc.;
(f) is easy and economical to manufacture;
(g) is simple to install on existing airplanes;
(h) is simple to use;
(i) can be used independently of the launching mechanism; and
(j) does not affect the aesthetic appearance of the aircraft.
In keeping with these objects, and with others which will become apparent hereinafter, one feature of the present invention resides in an automatic pilot system comprising one or more flexible control elements of the same basic design, wherein each control element constitutes a single-piece structure so that the means for sensing the relative wind speed, and the means for adjusting the control surface accordingly are provided solely by the geometric design and the material of the control element. The energy for the adjustment of the control surface is derived from the kinetic energy of the wind.
Another feature of the present invention is that, depending on its location on the aircraft, such a flexible control element can act as an automatic rudder, an automatic elevator, or an automatic wing tip.
Still another feature of the present invention is that the automatic pilot system might, in addition to the flexible control elements, also comprise a movable weight, such as a screw, concealed inside the nose of the fuselage to provide means for pre-adjusting the aircraft""s gliding angle.
When the flexible control element is used as a rudder, it is set by the user before the launch according to the size of the desired gliding circles. During the high-speed take-off, the rudder automatically adjusts its position so that the glider can fly in a straight path. Once the gliding flight begins, the rudder assumes its preset position to guide the plane in a circular path.
When the flexible control element is used as an elevator, it adjusts its position automatically to provide a low angle of attack in order to minimize aerodynamic drag during the high-speed take-off. Upon the beginning of the free flight, the elevator adjusts itself to facilitate a low speed glide at the preset gliding angle. The automatic elevator is sensitive enough to detect the natural decrease in the prevailing wind speed, as the glider nears the ground. Therefore, it adjusts its position so that the glider""s nose is slightly raised and the glider lands at a near horizontal attitude, and a reduced speed.
When a pair of flexible control elements are used as flexible dihedral wing tips, they enhance lateral stability throughout the flight. During normal flight, a small dihedral angle on both wing tips is enough to assure lateral stability of the aircraft, while permitting easy banking turns. If turbulence causes a sideslip, and the strength of a disturbing lateral wind increases, the wing tips automatically increase their dihedral angles in an asymmetrical fashion, so the plane quickly resumes its horizontal position. During take-off, the wing tips increase their dihedral angles symmetrically to avoid dangerous sideslips at a high speed.
When all of the above three types of control elements are used on the same aircraft, the resulting pilot system provides full three-axis automatic control. However, since the individual control elements function completely independent of each other, a user can choose to use one, two, or all three types of them. The weight of the complete automatic pilot system in its preferred embodiment is only about ten grams, thus it can be used even on gliders made of very light material, such as plastic foam.
Since the means for sensing the wind speed and the means for positioning the control surfaces are integrated into a single piece structure in each control element, the present automatic pilot system contains no parts, such as hinges, links, rubber bands etc., that are costly to manufacture and difficult to assemble. The single-piece control elements can be inexpensively manufactured and easily attached to existing model gliders that do not have a moving rudder or a moving elevator.
Since all visible components of the present automatic pilot system can be made of clear plastic, they do not detract from the overall appearance and elegant aerodynamic shape of a well designed glider. Furthermore, they can be used on flying toys shaped other than an airplane, such as birds, fictional characters, etc., that would not normally have rudders, elevators, or wing tips.
On model gliders launched by a tow line, this invention is recommended to be used in combination with the automatic tow release system described in our U.S. Pat. No. 6,336,838. The flight performance of a glider obtained by the combined use of these control systems is similar to that obtained by the use of a radio control system. One significant difference is that the same flight performance and enjoyment is obtained at a much reduced cost.
Additional detailed features of the invention will be best understood from the following description of the preferred embodiments and their accompanying drawings.